Metal pipes are widely used in engineering machinery, automobile industry, petrochemical industry, agricultural and animal husbandry machinery and other industries. Due to different application scenarios, parts need to be processed into different shapes and sizes to meet the needs of different industries.
Laser processing technology is particularly suitable for the processing of various metal pipes. The pipe laser cutting system has the characteristics of high flexibility and high automation and can realize the production mode of small batches and multiple varieties of different materials.
Perforation is often encountered in laser cutting processing. What we call laser cutting perforation refers to making a small hole in the plate. The main application area is precision instruments and equipment. In the early days of laser stamping composite machines, a punch was used to punch out a hole, and then the laser was used to cut from the small hole. As laser power continues to increase and the process matures, direct laser perforation has become mainstream. So what are the laser cutting and perforation methods?
1. Blast and perforate. After the material is irradiated by continuous laser, a pit is formed in the center. Then the molten material is quickly removed by the oxygen flow coaxial with the laser beam to form a hole. Generally, the size of the hole is related to the thickness of the plate. The average diameter of the blasting perforation is half of the plate thickness. Therefore, the blasting perforation hole diameter of the thicker plate is larger and not round. It is not suitable to be used on parts with high processing accuracy requirements. It can only be used on waste. In addition, since the oxygen pressure used for perforation is the same as that used for cutting, the splash will be larger.
2. Pulse perforation – laser cutting machine uses high peak power pulse laser to melt or vaporize a small amount of material. Air or nitrogen is often used as auxiliary gas to reduce hole expansion due to exothermic oxidation. The gas pressure is smaller than the oxygen pressure during cutting. Each pulse of the laser produces only small jets of particles that penetrate deeper gradually, so thick plate piercing takes a few seconds.
Once the piercing is completed, immediately change the auxiliary gas to oxygen for cutting. The advantage is that the quality is better, but the disadvantage is that the cost is relatively high, and a more reliable air path control system is required. The laser used for this purpose should not only have high output power; more importantly, it should have the time and space characteristics of the beam. Therefore, general cross-flow CO2 lasers cannot meet the requirements of laser cutting. In addition, pulse perforation also requires a more reliable gas circuit control system to achieve switching of gas types, gas pressure and control of perforation time.
The above two different perforation methods are suitable for different places. Generally, the size of the hole is related to the thickness of the plate. The average diameter of the blasting perforation is half of the plate thickness. Therefore, the blasting perforation hole diameter of the thicker plate is larger and not round, so it is not suitable When used on parts with higher requirements (such as petroleum screen slot pipes), it can only be used on scrap materials.
In addition, since the oxygen pressure used for perforation is the same as that used for cutting, the splash will be larger. However, theoretically speaking, it is usually possible to change the cutting conditions of the acceleration section, such as focal length, nozzle position, gas pressure, etc., but in fact it is unlikely to change the above conditions because the time is too short. In industrial production, it is more realistic to mainly use the method of changing the average cutting power. There are three specific methods:
(1) Change the pulse width;
(2) Change the pulse frequency;
(3) Change pulse width and frequency at the same time.
Therefore, in summary, after comparing the cutting and perforation technology of laser cutting machines, it can be found that the pulse perforation used by laser cutting machines has better perforation quality than blast perforation, and the perforation quality is also related to the power of the laser cutting machine.
So in the actual processing process, how should we choose the processing method according to the actual situation? When processing small holes, we do not use blasting and perforation, but pulse perforation (soft puncture), which makes the laser energy Too much concentration in a small area will burn the non-processed area, causing hole deformation and affecting the processing quality.
Therefore, we must choose the perforation method reasonably according to our actual situation. Not every method is suitable for all processes.
3. Technical analysis of laser cutting and perforation applications
In the case of pulse perforation, in order to obtain high-quality cuts, the transition technology from pulse perforation when the workpiece is stationary to constant-speed continuous cutting of the workpiece should be paid attention to. Theoretically, it is usually possible to change the cutting conditions of the acceleration section, such as focal length, nozzle position, gas pressure, etc., but in fact it is unlikely to change the above conditions because the time is too short. In industrial production, it is more realistic to mainly use the method of changing the average laser power. The specific methods are to change the pulse width; change the pulse frequency; and change the pulse width and frequency at the same time.
- How to solve the deformation of small holes in laser cutting?
The phenomenon of deformation of small holes in cutting and processing occurs mainly because the machine tool (only for high-power laser cutting machines) does not use blasting and perforation when processing small holes, but uses pulse perforation (soft puncture), which makes the laser energy Too much concentration in a small area will burn the non-processed area, causing hole deformation and affecting the processing quality. At this time, we should change the pulse perforation (soft puncture) method to the blast perforation (ordinary puncture) method in the processing program to solve the problem. For lower power laser cutting, it is just the opposite. When processing small holes, pulse perforation should be used to achieve better surface finish.
- How to solve the perforation slag during laser cutting?
During the perforation process of thick plates processed by laser, there is a phenomenon of slag accumulation. If it is cut directly, it will lead to problems such as poor cutting quality and rough cutting section. Currently, there are two commonly used cutting methods to reduce slag on the market: slow start and increasing cutting follow-up speed. Slow starting cutting speed will affect the service life of the nozzle, thereby increasing the customer’s processing cost; increasing the cutting follow-up speed will cause the cutting surface effect to decrease and affect product quality. “How to handle cutting and processing slag with high quality, efficiency and low cost” has become an urgent problem that needs to be solved in the laser industry.